Pore-size control of soft mesoporous carbon by hot pressing

抄録

As a simple post-synthesis approach for the mesopore-size control of nanoporous carbons, we propose mechanical pressing of soft carbons at 600 °C, i.e. hot pressing. Although conventional nanoporous carbons are mechanically hard and brittle, a carbon mesosponge (CMS), which is primarily composed of randomly arranged graphene walls, is exceptionally soft with a record low bulk modulus of 0.084 GPa for a solid carbon material. As a result, its mesopores with an average size of 7.36 nm, can be made smaller by applying a small mechanical pressure of only 10 MPa. Interestingly, the specific surface area and pore volume of the CMS increase when a small mechanical pressure (<20 MPa) is applied. This is attributed to the exfoliation of weakly stacked graphene structures generated during CMS synthesis. Moreover, the average mesopore size of the CMS can be finely changed to be as small as 2.14 nm using a carefully adjusted mechanical pressure. We report structural changes that occur during the hot pressing of a CMS, focusing on its crystallinity, graphene edge sites, and framework flexibility. Although the CMS framework hardens on application of a mechanical force, it still retains its low bulk modulus. Thus, the hot pressing of CMS provides a simple method for fabricating soft and elastic mesoporous carbons with controllable mesopore sizes between 2.14 and 7.36 nm.